1. Field of the Invention
The present invention relates to a titanium-based alloy consisting of a hard phase, a binder phase and unavoidable impurities, and more particularly, it relates to a titanium carbonitride-based alloy which is excellent in chipping resistance and wear resistance.
2. Description of the Prior Art
A titanium carbonitride-based alloy (cermet), which is superior in oxidation resistance and wear resistance to a WC-based alloy, is widely applied to a cutting tool. However, the conventional cermet having the aforementioned advantages is readily mechanically chipped.
When observing the structure of the conventional cermet with a scanning electron microscope, it is observed that particles forming the hard phase in the alloy have black core parts which are located on core portions to appear black and peripheral parts which are located around the black core parts to appear gray. In every hard phase particle, the ratio of the area of the black part to that of the peripheral part is substantially constant. If the areas of the black core parts in the respective particles are relatively large, the alloy is improved in wear resistance but deteriorated in chipping resistance. If the areas of the black parts in the respective particles are small, on the other hand, the alloy is improved in chipping resistance but deteriorated in wear resistance. It is difficult for the conventional cermet to have excellent characteristics in both of chipping resistance and wear resistance.
Japanese Patent Laying-Open No. 62-170452 (1987) discloses cermet comprising a hard phase having a cored structure. The hard phase consists of particles having black core portions and those having white core portions. The black core portions have abundance of a metal such as Ti belonging to the group IVa of the periodic table, and the white core portions have abundance of a metal such as W belonging to the group Va or VIa. In the cermet disclosed in the aforementioned gazette, the hard phase particles having the black core portions and those having the white core portions are dispersed in a constant ratio. However, the hard phase particles having the white core portions hardly contribute to wear resistance of the cermet. The hard phase particles having the white core portions occupy a large ratio of 50 to 80% with respect to the overall hard phase, to result in insufficient wear resistance of the cermet.